Cam for square-hole drills.



G. E. OTIS.

CAM FOR SQUARE HOLE DRILLS.

APPLICATION FILED JAN. 17.1917.

Patented May 14,1918.

2 SHEEIS-SHEET1 7 1' i.

. H V 1|. u m 4 G. E. OTIS.

CAM FOR SQUARE HOLE DRILLS.

A APPLICATION FILED mu. 17. $911.

Patented May 14, 1918.

2 SHEETSSHET 2.

GERALD E. OTIS, OF BUFFALO, NEW YORK, ASSIGNOR 'IO ANGULAR DRILL & MACHINE CORPORATION, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK. I

CAM FOR SQUARE-HOLE DRI-IJIAS.

Specification of Letters Patent.

Patented May 14, 1918.

Application filed January 17, 1917. Serial No. 142,882.

To all whom it may concern:

Be it known that I, GERALD E. OTIS, a citizen of the United States of America, and a resident of Bufialo, Erie county, and State of New York, have invented certain new and useful Improvements in Cams for Square-Hole Drills, of which the following is a specification, reference being had to the accompanying drawings, forming a part thereof.

My invention relates to cams for square hole drills and its object is to improve the form of the drill shank cam and to provide a cam which shall be more efficient than those heretofore available.

In order that my invention may be thoroughly understood, I willv now proceed to describe the same in the following specification, and then point out the novel features thereof in appended claims.

Referring to the drawings:

Figures 1 and 2 are diagrammatic plan views of square hole drill cams, such as have been known heretofore.

Fig. 3 is a similar representation of a hypothetical cam built up around a triangle having one of its angles less than and Fig. 4: is a view of a part of the out such a cam would produce.

Fig. 5 is a hypothetical cam built up around a similar triangle with its smallest angle theoretically reducedto 0.

Fig. 6 is a similar view of a cam built up around a triangle having one of its angles greater than 90.

Fig. 7 is a hypothetical cam built up around a similar triangle with its greatest angle theoretically increased to 180.

Fig. 8 is a diagrammatic plan view of a cam made accordingto and embodying my present invention.

Like characters of reference designate corresponding parts in all the figures.

It has been known for many-years that a drill shank constructed to have a cam shape built up around an equilateral triangle, when rotated without lost motion within a guide hole of square cross-section, would cause the bit of such drill to cut an approximately square hole. The sides of the shank cam have been made convex, usually on curves struck from each of the apexes of the triangle 0 and intersecting at the other apexes. Such a cam is shown in Fig. 1.

In all of the figures the triangle around which the cams are constructed is shown by light solid lines, and in Fig. 1 its angles or apexes are designated by the reference letters A, B and C. The cam perimeters in all of the figures of the drawings, are shown by dash and dot lines which in Fig. 1 are designated by the reference letters D, E and F. A square is circumscribed around the cams by light solid lines and designated in Figs. 17 by the reference letter G. This represents the square sectioned guide for the drill cam. The hole drilled by the various cams shown is illustrated by dotted lines. With the cam shown in Fig. 1 the drilled hole will correspond with the square G, except at the corners where a curved fillet will be formed designated H. It is assumed that the end of the cutting edge of the tool is in every case in the vertex of the angle opposite the base of the triangle, which base in Fig. 1 is assumed to be the side B, C, so that'the end of the cutting edge is at the point A. This angle may be termed the governing angle of the cam be-' cause the path taken by the point A in a revolution'determines the shape of the hole to be drilled. i

The fillets H of Fig. l are formed because of the fact that there is a time during the revolution of the cam in its square guide when no part of the arc'D remains tangent to one side of the square G. T

The fillet left by such a device makes its use objectionable.

It has been discovered that a square hole without fillets may be drilled by so constructing a cam that the arc having the governing angle as a center will at all parts of a revolution, remain tangent to one or another of the sides of a square guide. Such a cam can be built up only around a 90 isosceles triangle, and such a cam is illustrated in Fig. 2.

In this Fig. 2, A" is the 90 governing angle ofthe triangle and its other apexes are designated by B and C. D is an are drawn from A as a center and with a radius equal to the side A B of the triangle.

E is an arc drawn from B as a center and with a radius equal to the side B- C of the triangle, and F is a similar are described from C as a center. In this case a fourth arc, described from ,A as a center and of a radius, equal to the difi'erence between the side A B of the triangle, and one side of the square G joins the arcs E and F to complete the perimeter of the rain.

When such a cam is rotated without lost inotion within a square guide G. its governing angle A will describe a square path .l:

considerably smaller than the guide. but

used as a ease for a cam of this general charactor. For the sake of symmetry and ease of demonstration, I will lnnit this descrip tion to cams built up around isosceles tr1 angfles. It has been shown that when the governingangle is reduced from 90 to 60 (Figs. 2 and 1), the drilled holechanges t'roinasquare to a square-sided figure with cui'vedfillets in its corners. When the governing angle is'inade less than 60 the flat sides decrease and the fillets increase proportionately. Fig. 3 is an example of a cain built up around an isosceles triangle having a governing angle of In this case the fiat sides of the drilled hole will be of the length shown at H in Fig. a, and the fillets of the size shown at H -in Fig. 3.

It the governing angle is theoretically reduced to 0, as at A in Fig. l, the other *apexes B and C of the triangle will coini cide and the earn outline shown as in the other figures by a dash-and dot line and designated by J, is a circle. riith such a cam the'point A obviously rotates in a circular path ll" which coincides with the circle J and the hole it would cut would have no lat sides.

Fig. 6 showsthat it the governing angle at BB is made greater tian 90, the cam built up around it would' cause the point A to travel in a square path H much smaller than the guide.

Fig. 7 is a continuation of this idea and shows what would happen it the overning angle A? is enlarged to 180 in which case the cam would be a circle with the-point A in its center-so that this point would not more when the e-am was rotated.

In the two examples of the former art,

1: and 2,and in the hypothetical cases illustrated in Figs. 3, 'l. 5, 0 and 7, the

perinieter of the cam consists of three or more connected arcs, describedfrom the wertices of the triangle as centers, and inclosin the respective interior angles of the triang e together with such exterior arcs as may be necessary to coinpletethe perimeter.

periineter will contain atotal of sir; and centers. The pernneter of a o-tun Wlll" contain at least one center but since Any there are only three centers, it must also contain three arcs or more. The perimeter of a 60 cam will contain three arcs and three centers; tor-more than 60 and less than l8O ,..t'our arcs and two centers; for less than 60 and more than 0, tire arcs and one center. In outlines larger than the critical outline, all of the elements will he arcsywhiie tlie threc centers will lie within the cam. From a practicalstandpoint,in drilling square *llOlQS CiiDlS-Of 60 and'less are unsatisfactory for general use because they leave too large a filletinthe cornersot the hole. Cains with the governing angle 30 or more are unsatisfactory because they produce an unsteady movement of the tool because ot the period of rest. 1 have-found that the best results are obtainedby the use of a cam based upon a critical outline built up around an isosceles triangle having a got-'erning angle of more than 60 and less than 909. Such-a cam is shown-imFig. 8. in this figure the triangle is designated by A, B C of which the angle at the vertex A is the governing angle and is of if more than 60 and less than 90 'The are is described from A as acenteron a radius A,

.9 lhe are E described-from B as acenter on a rachus B 0 and F 18 21 similararc described from C asa center. Atourth are I from A as-a center joins the arcs E" and F. The perimeter thus formed and-shown by a dash and dot-line is :What lea-ll the critical outline of the cainand a care o't-this-ioo form will cause the governing angle A to travel on the pa'th H shown by a :dotted line. This is approximately a perfect-square with verysmall fillets in its corners. The fillets are not large enough to be objection able and the tool will not stop-intermit- 'tently during its-rotation.

A earn made toeorrespond withthis critical outline will wear at l t-S sharp corners,

' the vertices B and c -andthese sharp'con' ners will scrape and wear the surface-ofthe square guide. TlllS-ObjQCtlOIlfiblfi feature may he oi'erconie by making the camlarger than the critical outline and 1 providing for It a larger square guide.

- ihis isdone by describnig arcs DEE-11F and I concentric with and equi-distant from corresponding: parts of 1 the critical 1 "outline and joining the ends of'aro D 'with adjac'enten'ds of arcs l3 and F oy-arcs K and L drawn from the-apex'es B -and C The shape of the cam" will then he' that shown lay-the heavy black line-of- Fig: 8 and will cause a hole-to be cut ofthe tormshow by the dotted line H. l hissanie' means of so constructing a ea-m that it "willhave no sharpcorners, may of course, beapplicd as well to canis'built up around other than such triangles as that shown in Fig. 8, and therefore I do notliniit 13C this part of my invention to a cam which is constructed around an isosceles triangle having its governing angle greater than 60 and less than 90.

What I claim is:

1. A cam for square hole drills having arcs described from the vertices of an isosceles triangle having an angle between the equal sides thereof greater than 60 and less than 90.

2. A cam for square hole drills having major arcs described from the vertices of an isosceles trianglehaving an angle between the equal sides thereof greater than 60 and less than 90 and with minor arcs drawn from the vertices of said triangle and joining the ends of said major arcs.

3. A cam for square hole drills having major arcs described from the vertices of a triangle with greater radii than the length 20 GERALD E. OTIS.

Ccpies of this patent may be obtained for five cents each, by addressing the Commissioner of Patents, Washington, D. G. 

